The invention relates to practical applications of signal quality observations in a wireless communication network. Signal quality observations are primarily used to select a cell or base station in a wireless communication network. The invention is particularly related to other uses of signal quality observations, such as mobile positioning and network planning.
It has recently been discovered that observations of signal quality, such as signal strength, bit error rate/ratio, signal-to-noise ratio, and the like, can be used to locate a mobile communication device. As used herein, the term ‘target device’ refers to a mobile communication device whose location is to be determined.
FIG. 1 schematically illustrates an example of such a positioning technique. A target device T communicates via base stations BS via a radio interface RI. In this example, the communication is assumed to be radio communication. The target device T observes signal values at the radio interface RI. The observations O are applied to a probabilistic model PM that models the target device's wireless communication environment and produces a location estimate LE. As used herein, a target device is a device whose location is to be determined. The target device communicates via signals in a wireless environment, and signal values in the wireless environment are used for determining the target device's location. For example, the target device may be a data processing device communicating in a wireless local-area network (WLAN). The data processing device may be a general-purpose laptop or palmtop computer or a communication device, or it may be a dedicated test or measurement apparatus such as a hospital instrument connected to the WLAN. A location, as used herein, is a coordinate set of one to three coordinates. In some special cases, such as tunnels, a single coordinate may be sufficient but in most cases the location is expressed by a coordinate pair (x, y or angle/radius).
Mobile communication devices measure signal quality parameters. A good example of a signal quality parameter is signal strength. An acronym RSSI is frequently used to refer to a received signal strength indicator. The RSSI is used, for example, to select a cell or base station.
A problem associated with the above-described prior art technique is the fact that many mobile communication devices measure the signal strength or RSSI rather poorly. The primary use of the RSSI is to select an optimal cell or base station, and a rather coarse measurement suffices for that purpose. When the RSSI (or any other signal value) is used for positioning or network planning, far better accuracy is desired. Further, as the primary use of the RSSI is to select an optimal cell or base station, the RSSI measurement may be grossly inaccurate when the signal strength is high, because in such a situation there is no need to change the serving cell or base station. A related problem is encountered in network planning and/or maintenance.